FAQ: Open Source Battery Management System (BMS)
How much does the Open BMS cost to manufacture?
The current production cost of the BMS at prototype scale (~25 pieces), including cables, the temperature sensor and connectors, cost LibreSolar 140 euros in Germany. For larger quantities, the manufacturing cost would significantly go down and is expected to be around 50 Euros. For lower needs in maximum current, even less. We estimate that cheaper components (like the terminals) could be available. Or if you have an integrated solution where you already know where the cables are going, you could easily change the BMS design a bit, spare the terminals completely and solder the wires directly onto the board, which could also save costs.
The price is about 400 to 500 euros for off-the-shelf proprietary BMS systems with comparable technical specifications.
Is it possible to manufacture the PCBA locally? What equipment is required?
The BMS was designed in such a way that it can be manually assembled, making local manufacturing more accessible. It contains almost entirely just SMD parts (surface mount devices and not the older through-hole technology). Soldering them manually is still possible. So either you can use tweezers, or if you have access to a (manual) pick and place machine, it becomes a little bit easier.
It takes a while, but it's possible to assemble and do re-work by hand. For materials, you need the PCB and the parts, and you will need a stencil to apply the solar paste. These are used to connect the parts with the PCB and the process is that you apply the solar paste with the stencil, then you place the parts and afterwards you put the whole assembly in into a reflow open, a temperature profile of up to 250 degrees is applied, and then the PCBA is ready.
These reflow ovens are not very expensive. The reflow oven Libre Solar uses costs about 250 euros.
The manufacturing is possible on a small scale by hand but it is only recommended for prototyping. Once your prototype is in place, you can use an automatic pick-and-place machine and some more professional equipment. Libre Solar used SMD connectors because it made the assembly to the heat sink easier and reduced one of the manufacturing steps (which means one less machine). However these connectors to the heat sink have quite a huge thermal mass.